The reagents used for dehydration of alcohols

(A) Conc. $H_2SO_4$
(B) Phosphoric acid
(C) Alumina
(D) Anhydrous $ZnCl_2$

Choose the correct answer from the options given below:

(A), (B), (C) and (D)

The correct answer is Option (3) → (A), (B), (C) and (D)

• (A) Conc. H₂SO₄: Classic reagent, especially for primary alcohols at high temperature (e.g., ethanol → ethene at ~170°C).
• (B) Phosphoric acid (H₃PO₄): Widely used (often concentrated), particularly in industrial processes or for secondary/tertiary alcohols.
• (C) Alumina (Al₂O₃): Effective as a heterogeneous catalyst, especially in gas-phase dehydration at high temperatures (e.g., ethanol over heated alumina).
• (D) Anhydrous ZnCl₂: Used particularly with conc. HCl for primary alcohols (Lucas reagent context), but anhydrous ZnCl₂ alone (or with alcohol) facilitates dehydration, especially for tertiary and secondary alcohols.

Thus, (A), (B), (C) and (D) are correct.